Seems to be a gremlin in the game, I have a ex offy that I am now under, He has no commander the person who he is trying to join is not a offy of his or was connected to him last age and when he trys to join them he is getting this message

Error
You may not choose a commander who can be found in your officer tree.

anybody else getting anything like this, and is their anything that can be done to solve it